1. Field of Invention
Aspects of the present invention relate to a method of removing organic chemicals and organometallic complexes from wastewater. More particularly, aspects of the present invention relate to a method of removing organic chemicals and organometallic complexes (organic heavy metal complexes) using zeolite from process water or tailings streams of a mineral processing plant where diethylenetriamine (DETA) or triethylenetetramine (TETA) is used as a flotation reagent and DETA-metal complexes are found in process water or tailings streams.
2. Description of Related Art
DETA (Diethylenetriamine) has conventionally been used to assist with the selective separation of minerals, such as pentlandite, from the waste mineral pyrrhotite. It is generally important to achieve a target concentrate reagent grade at the desired recovery when processing complex sulphide ores. DETA is a strong chelating agent and it can form very stable complexes with heavy metal ions (Cu2+ and Ni2+) in solution.
Conventional wastewater treatment methods, which generally involve raising the pH above 9.5 with lime to form metal hydroxide precipitates, is not effective when DETA-Cu/Ni complexes are present, even at pH 12. In order to be able to use DETA dosages to reach a desirable level of pyrrhotite rejection in the mineral processing step without generating excessive amounts of heavy metals in the effluent, an effective method is required to remove DETA and its complexes from the process water or contain it in the tailings area.
Natural zeolites are microporous crystalline aluminosilicates with well-defined structures in that silicon and aluminium atoms are tetrahedrally coordinated with each other through shared oxygen atoms to form a regular framework. With their unique porous properties, wide availability, low cost and high efficiency, natural zeolites are used in a variety of applications with a global market of several million tonnes per year. The major uses of natural zeolites are in petrochemical cracking as catalysts, in the separation and removal of gases and solvents, and ion-exchange applications in water softening, purification, heavy metal removal and nuclear effluent treatment because exchangeable ions in zeolite (sodium, calcium and potassium ions) are relatively innocuous. Other applications for zeolites, such as filtration, odor control, and desiccation, are also found in aquaculture, agriculture and animal husbandry. For example, clinoptilolite zeolite (a typical natural zeolite) has been studied extensively as an ion exchanger and is commercially used in the treatment of industrial and municipal wastewaters to reduce the concentration of ammonia.
However, most of the studies about ion exchange with zeolite have focused on the removal of free metal/ammonium ions from the wastewater of electroplating shops, in some cases through the addition of polyamines such as DETA to the wastewater. For example, U.S. Pat. No. 4,167,481 discloses a process for removal of metals from metal-containing solutions comprising adding to the solution a polyamine and contacting the solution with a cation exchanger selected from tectosilicates or phyllosilicates; and U.S. Pat. No. 5,500,126 discloses a process for removal of metal ions from metal plating waste streams comprising adding to the solution a polyamine in an amount of 0.1 to 0.5 times the metal concentration and contacting the aqueous solution with a cation exchanger.
It should be noted that the state of the art is silent regarding the use of zeolite in the removal of organic chemicals, such as DETA, and chelated metal organic molecules, such as DETA-Cu/Ni complexes from the process water or slurry tailings streams of mineral processing plants. In this case, DETA and DETA-metal complexes are present in the process water and slurry tailings streams due to the DETA additions made as part of the mineral processing steps and have to be removed or controlled. The process water and slurry tailings streams generally contain residual amounts of flotation chemicals and have relatively high levels of Ca and Mg ions, which may affect the adsorption of heavy metals on zeolite.